Hybrid bipolar plate for fuel cell

ABSTRACT

A hybrid bipolar plate assembly for a fuel cell includes a formed cathode half plate and a stamped metal anode half plate. The stamped metal anode half plate is nested with and affixed to the formed cathode half plate. Each of the half plates has a reactant side and a coolant side, a feed region, and a header with a plurality of header apertures. The coolant side of the formed cathode half plate has support features that can be different from and need not correspond with cathode flow channels formed on the opposite reactant side. The coolant side of the stamped metal anode half plate has lands corresponding with anode channels formed on the opposite oxidant side. The lands define a plurality of coolant channels on the coolant side of the stamped metal anode half plate and abut the coolant side of the formed cathode half plate.

FIELD

The present disclosure relates to fuel cell stacks and, moreparticularly, to a bipolar plate assembly for fuel cell stacks.

BACKGROUND

A fuel cell has been proposed as a clean, efficient and environmentallyresponsible power source for various industries, including manufacturingcenters, homes, and electric vehicles among other applications.

One example of the fuel cell is a Proton Exchange Membrane (PEM) fuelcell. The PEM fuel cell includes a membrane-electrode-assembly (MEA)that generally has a thin, solid polymer membrane-electrolyte having ananode and a cathode with a catalyst on opposite faces of themembrane-electrolyte. The MEA is generally disposed between a pair ofporous conductive materials, also known as gas diffusion media, whichdistribute gaseous reactants, for example, hydrogen and oxygen or air,to the anode and cathode layers. The hydrogen reactant is introduced atthe anode where it reacts electrochemically in the presence of thecatalyst to produce electrons and protons. The electrons are conductedfrom the anode to the cathode through an electrical circuit disposedtherebetween. Simultaneously, the protons pass through the electrolyteto the cathode where an oxidant, such as oxygen or air, reactselectrochemically in the presence of the electrolyte and catalyst toproduce oxygen anions. The oxygen anions react with the protons to formwater as a reaction product.

The MEA of the PEM fuel cell is sandwiched between a pair ofelectrically-conductive bipolar plates which serve as current collectorsfor the anode and cathode layers. The bipolar plates contain and directfluids into, within and out of the fuel cell, and distribute fluids tofull cell areas necessary for operation. Also, bipolar plates providestructural support for diffusion media, membranes, seals, etc. Theyfurthermore enable sealing from one fuel cell to the next, conduct heatformed by reactions within the fuel cell, and importantly also conductelectricity generated by the fuel cell reactions.

In particular, the bipolar plates include a plurality of lands and flowchannels for distributing the gaseous reactants to the anodes andcathodes of the fuel cell. The bipolar plates serve as an electricalconductor between adjacent fuel cells and are further provided with aplurality of internal coolant channels adapted to exchange heat with thefuel cell when a coolant flows therethrough.

A conventional bipolar plate is a joined assembly constructed from twoseparate unipolar or half plates. Each half plate may have an exteriorsurface with flow channels for the gaseous reactants and an interiorsurface with the coolant channels. In order to conduct electricalcurrent between the anodes and cathodes of adjacent fuel cells in thefuel cell stack, the paired half plates forming each bipolar plateassembly are mechanically and electrically joined. For example, suchbipolar plates are commonly constructed having the pair of half platesjoined by adhesive seal, by brazing, or by welding.

It is known to form bipolar plates from either carbon compositematerials or metallic metals. Each approach has advantages andlimitations. Nested composites are described in U.S. Pat. No. 7,029,784to Carlstrom. Nested stamped metal and non-nested composite and stampedmetal bipolar plates have been proposed in U.S. Pat. No. 6,974,648 toGoebel, and U.S. Pat. No. 7,687,175 to Abd Elhamid et al., respectively.Feed region support for nested plates has also been described in U.S.Pat. No. 7,291,414 to Goebel. The entire disclosures of these patentsare hereby incorporated herein by reference. However, none of theseknown bipolar plates retain the advantages of combining a formed cathodehalf plate with a stamped metal anode half plate as disclosed herein.

There is a continuing need for a hybrid bipolar plate assembly thatretains the advantages of a formed bipolar plate half and a stampedmetal bipolar plate half. Desirably the hybrid bipolar plate assembly isthin but can support very high current densities.

SUMMARY

In concordance with the instant disclosure, a hybrid bipolar plateassembly that retains the advantages of both a formed bipolar plate anda stamped metal bipolar plate, and which is thin but can support veryhigh current densities, is surprisingly discovered.

As used herein, the term “formed half plate” refers to a solid platehalf with channels formed therein. The formed half plate is typicallyformed of a carbon composite material but may also be formed ofgraphite, graphite filled with resin or even machined or etched metalssuch as stainless steel or titanium.

As used herein, the term “tunnels” refers to covered channels disposedunder a seal to allow fluid (e.g., hydrogen, air or oxygen, and coolant)to flow from and to its respective header of the fuel cell.

As used herein, the term “feed region” refers to a cross-flow regionwhere different fluids (e.g., hydrogen, air or oxygen, and coolant) areflowing in different directions simultaneously during operation of thefuel cell. The feed region is needed in order to distribute flows fromindividual headers to a full width of a nested active area of the fuelcell.

As used herein, the term “active area” refers to an area of the fuelcell where are necessary components for the fuel cell operation areavailable, namely, hydrogen, air or oxygen, coolant, polymer electrolytemembrane, catalyst, electrical conductor (e.g., diffusion media), andelectrical contact (e.g., all necessary components under compression).Feed regions of nested plates are not considered to be in the activearea.

As used herein, the term “nested area” refers to a unique aspect ofstamped designs within the counter-flow active area region, where astamped metal anode half plate fits into a back of a formed cathode halfplate. In a non-aligned feed region, as the fuel cell repeat distance isvery small, and space is not available for all channels without removingdiffusion media from this region. In a nested plate design, the nestarea and the active area may coincide, and the feed region is non-activeas diffusion media is removed from this region.

As used herein, the term “membrane seal” refers to an entire perimeterof the fuel cell plate and headers where all three fluids (i.e.,hydrogen, air or oxygen, and coolant) are blocked from leaking overboardor from the headers at the interface to the membrane.

As used herein, the term “plate seal” refers to an entire perimeter ofthe fuel cell plate and reactants headers where all three fluids (i.e.hydrogen, air or oxygen, and coolant) are blocked from leaking overboardor from the headers at the interface between plate halves or half platesof the hybrid bipolar plate assembly.

In an exemplary embodiment, a hybrid bipolar plate assembly for a fuelcell includes a formed cathode half plate and a stamped metal anode halfplate. The formed cathode half plate has a reactant side and a coolantside, which are independent from each other. The reactant side of thecathode half plate may have fine pitch channels in an active area, feedchannels to cathode headers, port holes to cathode tunnels, and a sealgland around the perimeter and each of the headers. The reactant side ofthe cathode half plate has tunnels for all three fluids (i.e. reactant,oxygen or air, and coolant), with port holes from the cathode tunnels,and a feed region with support features such as an array of pillars andeither an open pocket to nest with the stamped metal anode half plate orsupport ribs aligned into every other stamped coolant channel.

The stamped metal anode half plate has a fuel side and a coolant side.The stamped metal anode half plate further a flat perimeter in a sealingregion, a bead feature along a coolant seal, port holes to anodetunnels, branched feed channels and straight channels through an activearea with an elevation change from feed to active area channels to nestinto the back of the composite cathode half plate.

Further, a membrane seal may be provided that is elastomeric and runsaround a perimeter of the bipolar plate and each of the headers. Theplate seal follows a same perimeter path but is more inboard in front ofthe reactant headers and is not needed in front of the coolant header.This plate seal may be elastomeric, compressible graphite, or epoxy, asnon-limiting examples. The plate seal is narrower in front of the anodeheader to allow tunnel flow to the anode ports. Alternatively, a widersupport region may be used. The location of the diffusion media does notextend into the feed regions, in order to allow space for the stampedchannels to un-nest in the feed regions. The feed region may furtheremploy a membrane support shim.

In one embodiment, a hybrid bipolar plate assembly for a fuel cellincludes a formed cathode half plate and a stamped metal anode halfplate. The stamped metal anode half plate is nested with and affixed tothe formed cathode half plate. The formed cathode half plate has areactant side and a coolant side, a feed region, and a header with aplurality of header apertures. The reactant side has an active area. Theactive area has a plurality of cathode channels formed therein. The feedregion is disposed between the active area and the header and has aplurality of feed channels formed therein. The feed region also has aplurality of cathode port holes formed therethrough. The feed channelsare in communication with the cathode channels and the cathode portholes. The coolant side has a coolant distribution area disposedopposite the active area, and support features disposed opposite atleast one of the feed region and the active area. At least a portion ofthe coolant distribution area can be different from and need notcorrespond with the cathode flow channels of the active area.

The stamped metal anode half plate has a fuel side and a coolant side, afeed region, and a header with a plurality of header apertures. The fuelside has an active area. The active area has a plurality of anodechannels formed therein. The feed region is disposed between the activearea and the header and has a plurality of feed channels formed therein.The feed region also has a plurality of anode port holes formedtherethrough. The feed channels are in communication with the anodechannels and the anode port holes. The coolant side has a plurality oflands corresponding with the anode channels. The lands define aplurality of coolant channels on the coolant side of the stamped metalanode half plate. The plurality of lands abut the coolant side of theformed cathode half plate.

In another embodiment, the formed cathode half plate is formed fromgraphite, and the cathode channels of the formed cathode half plate havea pitch of about 1.5 mm or less. This particular fine pitch is believedto facilitate a very high current density, for example, of 1.5 to 2.5A/cm². The support features on the coolant side of the composite cathodehalf plate include a plurality of pillars extending outwardly from thecoolant side of the composite cathode half plate. The composite cathodehalf plate has a thickness of between about 0.3 mm and about 1 mm.

Additionally, the stamped metal anode half plate can be formed fromstainless steel or titanium and has a sealing region with a planarperimeter flange. The plurality of anode channels formed in the stampedmetal anode half plate include a plurality of branched feed channels inthe feed region of the stamped metal anode half plate and a plurality oflinear flow channels oriented along the active area of the stamped metalanode half plate. The stamped metal anode half plate has a thicknessthat is less than the thickness of the composite cathode half plate. Inparticular, the thickness of the stamped metal anode half plate may bebetween about 0.25 mm and about 0.55 mm.

In a further embodiment, a fuel cell stack having the hybrid bipolarplate assembly includes a plurality of membrane electrode assembliesarranged in a stacked configuration. Each of the membrane electrodeassemblies has a polymer electrolyte membrane with a cathode and ananode and associated diffusion medium layers. The hybrid bipolar plateassembly is disposed between adjacent membrane electrode assemblies. Themembrane electrode assemblies may further include a membrane seal andthe hybrid bipolar plate assemblies may include a plate seal. The plateseal is disposed between the formed cathode half plate and the stampedmetal anode half plate. The membrane seal and the plate seal areoverlaid and together circumscribe one of the diffusion medium layers. Aperimeter edge of the one of the diffusion medium layers is furthermorespaced apart from each of the membrane seal and the plate seal.

The membrane seal may be formed from an elastomer and disposed around aperimeter of the bipolar plate assembly and each of the headerapertures. The membrane seal may also be a weld joint if the compositeis selected to be a metal material. The plate seal may be formed fromone of an elastomer, a compressible graphite, and an epoxy material, andis also disposed around the perimeter of the bipolar plate assembly. Aportion of the plate seal adjacent one of the header apertures for theanode may also be thinner than a corresponding portion of the membraneseal adjacent the one of the header apertures for the anode. Thisarrangement permits tunnel flow to the anode port holes of the hybridbipolar plate assembly of the fuel cell stack.

It should be appreciated that the formed plates of the presentdisclosure can provide smaller or very fine channel features becausethey are not limited by the known “metal stretch” of stamped plates.This is particularly advantageous for reducing land width on the cathodeto improve performance. However, composite plates also usually requirethicker webs of, for example, about 0.3-0.5 mm. This can undesirablyaffect the fuel cell thickness, thus increasing the stack height andthereby limiting the number of cells which can be packed within spacelimited applications such as automotive. Nonetheless, it has beenrealized that formed plates do provide design flexibility becausedifferent channel patterns can be used on each side of the plate. Incontrast, for stamped metal plates, the negative image of the channelpattern is found on the opposite side of the half plate.

This ability to customize channel patterns in formed plates isparticularly advantageous in the tunnel and feed regions of the plates.For tunnels, channels are desired on the inside of the plate, while asmooth surface for sealing is required on the other side of the plate.Stamped plates require the use of staggered seals in the tunnel region,which require additional plate area. In the feed regions, the fluid mustflow in different directions to distribute the fluid to and from therespective headers. This limitation is particularly challenging for thecoolant flow of stamped metal plates because the coolant pattern is aresult of the cathode and anode patterns of on the opposite side of eachplate half.

Composite materials also provide reduced contact resistance and do notnecessarily require a contact coating such as gold, which is commonlyused on stamped metal plates. Graphite versions of composite platesprovide better in-plane thermal conductivity to support higher currentdensities and wider coolant channel spacing. Permeation of coolantoccurs through composite materials but not for metal. Water-glycolcoolant is typically used for applications exposed to sub 0° C.temperatures. However, the glycol of such water-glycol coolants canundesirably hinder catalytic reactions. This is less of an issue for thecathode side where the supplied air or oxygen can oxidize the glycol. Byusing a metal plate half on the anode side, the permeation of glycol tothe anode can be avoided where it would be more problematic.

For formed plates, the plate halves are also typically bonded togetherby epoxy while metal plates are welded together. The joint between theformed and metal plate halves requires a different approach such as anelastomeric seal, compressed graphite or compatible epoxy formulation,as described herein. It is also desired to use thin metal for thestamped plate half to reduce cost and weight; however, the stamped plateneeds to have adequate mechanical strength (i.e., adequate thickness) tosupport the compression loads need to reduce contact resistance withinthe fuel cell stack.

It has been surprisingly discovered that by combining a formed platewith a stamped plate, the advantages of the formed plate can beretained. The stamped plate half provides a reduction in bipolar platethickness and further, by nesting the stamped plate into the compositeplate, a substantial reduction in bipolar plate thickness can beachieved. Providing support ribs on the coolant side of the formed platehalf into every other coolant channel of the stamped plate half alsoallows the use of thinner metal for the stamped plate half.

DRAWINGS

The above, as well as other advantages of the present disclosure, willbecome readily apparent to those skilled in the art from the followingdetailed description, particularly when considered in the light of thedrawings described herein.

FIG. 1 illustrates a schematic, exploded perspective view of a PEM fuelcell stack, and shows only two cells with a single bipolar plateassembly for purpose of simplicity;

FIG. 2 is a top plan view of a formed cathode half plate for use in thebipolar plate assembly of FIG. 1, and further illustrating a reactantside of the formed cathode half plate;

FIG. 3 is a bottom plan view of the formed cathode half plate shown inFIG. 2, according to one embodiment of the disclosure, and furtherillustrating a coolant side of the formed cathode half plate with anarray of pillars in feed regions of the half plate and an empty pocketbetween the feed regions of the half plate;

FIG. 4 is a bottom plan view of the formed cathode half plate shown inFIG. 2, according to another embodiment of the disclosure, and furtherillustrating a coolant side of the formed cathode half plate withcoolant channel support ribs between feed regions of the half plate;

FIG. 5 is a top plan view of a stamped metal anode half plate for use inthe bipolar plate assembly of FIG. 1;

FIG. 6 is a fragmentary cross-sectional side elevational view of a fuelcell with an assembled bipolar plate assembly and taken along sectionline T-T of the anode half plate shown in FIG. 5, and with the anodehalf plate affixed to the cathode half plate shown in FIGS. 2 and 3 andassembled with a membrane electrode assembly (MEA), and furtherillustrating a long section view of a transition region of the fuelcell;

FIG. 7 is a fragmentary cross-sectional side elevational view of a fuelcell with an assembled bipolar plate assembly and taken along sectionline E-E of the anode half plate shown in FIG. 5, with the anode halfplate affixed to the cathode half plate shown in FIGS. 2 and 3 andassembled with an MEA, and further illustrating an unsupported coolantregion of the fuel cell;

FIG. 8 is a fragmentary cross-sectional side elevational view of a fuelcell with an assembled bipolar plate assembly and taken along sectionline E-E of the anode half plate shown in FIG. 5, with the anode halfplate affixed to the cathode half plate shown in FIGS. 2 and 4 andassembled with an MEA, and further illustrating coolant channel supportribs of the fuel cell;

FIG. 9 is a fragmentary cross-sectional side elevational view of a fuelcell with an assembled bipolar plate assembly and taken along sectionline C-C of the anode half plate shown in FIG. 5, with the anode halfplate affixed to the cathode half plate shown in FIGS. 2 and 3 andassembled with an MEA, and further illustrating cathode tunnels of thefuel cell;

FIG. 10 is a fragmentary cross-sectional side elevational view of a fuelcell with an assembled bipolar plate assembly and taken along sectionline A-A of the anode half plate shown in FIG. 5, the anode half plateaffixed to the cathode half plate shown in FIGS. 2 and 3 and assembledwith an MEA, and further illustrating anode tunnels of the fuel cell;

FIG. 11 is a fragmentary cross-sectional side elevational view of a fuelcell with an assembled bipolar plate assembly and taken along sectionline X-X of the anode half plate shown in FIG. 5, the anode half plateaffixed to the cathode half plate shown in FIGS. 2 and 3 and assembledwith an MEA, and further illustrating coolant tunnels of the fuel cell;

FIG. 12 is a top plan view of a plate seal for use with the fuel cellshown in FIGS. 1-11;

FIG. 13 is a top plan view of a membrane seal for use with the fuel cellshown in FIGS. 1-11; and

FIG. 14 is a top plan view of the plate seal shown in FIG. 12 shownoverlaid with the elastomeric membrane seal shown in FIG. 13 and adiffusion medium layer of the fuel cell, the plate seal shown withoutthe half plate for purposes of illustrating a relative lateralpositioning of the plate seal with the membrane seal.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould also be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features. Inrespect of the methods disclosed, the steps presented are exemplary innature, and thus, are not necessary or critical.

For simplicity, only a two-cell stack (i.e. one bipolar plate) isillustrated and described herein with respect to FIG. 1, it beingunderstood that a typical stack will have many more such cells andbipolar plates.

FIG. 1 depicts a two cell PEM fuel cell stack 2 having a pair ofmembrane-electrode-assemblies (MEAs) 4, 6 separated from each other byan electrically conductive fluid distribution element 8, hereinafteralso referred to as bipolar plate assembly 200. The MEAs 4, 6 include amembrane-electrolyte layer having an anode and a cathode with a catalyston opposite faces of the membrane-electrolyte. The MEAs 4, 6 and bipolarplate assembly 8, 200 are stacked together between end plates 10, 12 andend contact elements 14, 16 under compression. The end contact elements14,16 and the bipolar plate assembly 8, 200 include working faces 18,20, 22, 24, respectively, for distributing fuel and oxidant gases (e.g.,H₂ and Air or O₂) to the MEAs 4, 6. Nonconductive gaskets 26, 28, 30, 32provide seals and electrical insulation between the several componentsof the fuel cell stack 2.

The MEAs 4, 6 are disposed adjacent gas permeable conductive materialsknown as gas diffusion media 34, 36, 38, 40. The gas diffusion media 34,36, 38, 40 may include carbon or graphite diffusion paper. The gasdiffusion media 34, 36, 38, 40 contact the MEAs 4, 6, with each of theanode and the cathode having an associated one of the diffusion mediumlayers. The end contact units 14, 16 contacts the gas diffusion media34, 40 respectively. The bipolar plate assembly 8, 200 contacts the gasdiffusion media 36 on the anode face of MEA 4, configured to accepthydrogen-bearing reactant, and also contacts gas diffusion medium 38 onthe cathode face of MEA 6, configured to accept oxygen-bearing reactant.Oxygen is supplied to the cathode side of the fuel cell stack 2 fromstorage tank 46, for example, via an appropriate supply conduit 42.Hydrogen is supplied to the anode side of the fuel cell from a storagetank 48, for example, via an appropriate supply conduit 44.Alternatively, ambient air may be supplied to the cathode side as anoxygen source and hydrogen to the anode from a methanol or gasolinereformer, and the like. Exhaust conduits (not shown) for both the anodeand cathode sides of the MEAs 4, 6 are also provided. Additionalconduits 50, 52, 54 are provided for supplying liquid coolant to thebipolar plate assembly 8, 200 and end plates 14, 16. Appropriateconduits for exhausting coolant from the bipolar plate assembly 8, 200and end plates 14, 16 are also provided (not shown).

Referring next to FIGS. 2-14, the bipolar plate assembly 200 is shown ingreater detail. The bipolar plate assembly 200 includes a formed cathodehalf plate 202, for example, as shown in FIGS. 2-4, and a stamped metalanode half plate 204, for example, as shown in FIG. 5. In accordancewith the teaching of the present disclosure, the formed cathode halfplate 202 and the stamped metal anode half plate 204 are each formedfrom a different electrically conductive material, and according todifferent processes before being combined to form the bipolar plateassembly 200.

In particular, the formed cathode half plate 202 is formed from acomposite material. The composite material may be suitable for amanufacturing process such as machining, molding, etching, cutting, orcarving, as non-limiting examples. Suitable composite materials include,but are not limited to, graphite, graphite foil, conductive particles(e.g. graphite powders) in a polymer matrix, carbon fiber paper andpolymer laminates, metal plates, polymer plates with metal cores,conductively coated polymer plates, and combinations thereof, forexample.

The stamped metal anode half plate 204 is formed from a metallicmaterial suitable for use in a manufacturing process such as stamping.Suitable metallic materials include, for example, pure metals and metalalloys. The pure metals and metal alloys have sufficient durability andrigidity to function as sheets in the bipolar plate assembly 8 of thefuel cell stack 2. Suitable metals and metal alloys include, but are notlimited to, aluminum, titanium, platinum, stainless steel, carbon steel,nickel-based alloys, tantalum, niobium, and alloys and combinationsthereof.

Additional design properties considered in selecting a material for thecathode and anode half plates 202, 204 include gas permeability,conductivity, density, thermal conductivity, corrosion resistance,pattern definition, thermal and pattern stability, machinability,joinability, and availability. With these considerations, one ofordinary skill in the art may also select other suitable materials forthe formed cathode half plate 202 and the stamped metal anode half plate204, as desired.

Each of the formed cathode half plate 202 and the stamped metal anodehalf plate 204 has an optimized thickness, with the stamped metal anodehalf plate 204 being relatively thinner in thickness relative to theformed cathode half plate 202. For example, the composite cathode halfplate 202 may have a thickness of between about 0.3 mm and about 1 mm,more particularly between about 0.5 mm and about 0.75 mm, and mostparticularly about 0.65 mm. The stamped metal anode half plate 204 mayhave a thickness of between about 0.25 mm and about 0.55 mm, moreparticularly between about 0.35 mm and about 0.45 mm, and mostparticularly about 0.4 mm. One of ordinary skill in the art may alsoselect other suitable thicknesses for the formed cathode plate 202 andthe stamped metal anode half plate 204, as desired.

Being made from different materials, with the formed cathode half plate202 being formed from a composite material not generally conducive towelding or brazing operations, it should be understood that thecomposite cathode half plate 202 and the stamped metal anode half plate204 are affixed by other suitable means. Non-limiting examples ofsuitable means for affixing the half plates 202, 204 may include acompressed plate seal (shown in FIGS. 7-10 and 12 as “302”) disposedbetween perimeter flanges of each of the half plates 202, 204. Acompressed region of compliant graphite of the formed cathode half plate202 itself, where the formed cathode half plate 202 is formed fromgraphite, may also be employed to plate seal 302 and affix the halfplates 202, 204 to one another. Bonding of the formed cathode half plate202 with the stamped metal anode half plate 204 may also be accomplishedwith epoxy in the perimeter flange regions of the half plates 202, 204,for example, as shown in FIGS. 7-10. One of ordinary skill in the artmay also select other suitable means for affixing the formed cathodehalf plate 202 with the stamped metal anode half plate 204 within thescope of the present disclosure.

As shown in FIGS. 2-4, the formed cathode half plate 202 has a reactantside 206 (shown in FIG. 2) and a coolant side 208 (shown in FIGS. 3-4).The formed cathode half plate 202 further has a pair of feed regions210, 211 and a pair of headers 212, 213 with a plurality of headerapertures 214, 215. Although described primarily herewith with respectto a single one of the feed regions 210, a single one of headers 212,and a single set of header apertures 214 on one side of the formedcathode half plate 202, it should be appreciated that descriptions offeatures from the feed region 210, the header 212, and the headerapertures 214 likewise apply to the other feed region 211, the otherheader 213, and the other header apertures 215 shown in FIGS. 2-4.

With reference to FIG. 2, the reactant side 206 of the formed cathodehalf plate 202 has an active area 216. The active area 216 having aplurality of cathode channels 218 formed therein. The cathode channels218 are adapted to distribute the oxidant gases (e.g., air or oxygen)across the active area 216. The cathode channels 218 also define aplurality of lands 220 disposed therebetween.

The feed region 210 of the formed cathode half plate 202 is disposedbetween the active area 216 and the header 212. The feed region 210 hasa plurality of feed channels 222 formed therein. The feed channels 222also define a plurality of lands 224 disposed therebetween.

The feed region 210 of the formed cathode half plate 202 further hascathode port holes 226 formed therethrough, which are in turn incommunication with a one of the header apertures 214 associated with theoxidant gases. The feed channels 222 are in communication with both thecathode channels 218 and the cathode port holes 226. The feed channels222 are adapted to transport the oxidant gases between the active area216 and the one of the header apertures 214 associated with the oxidantgases.

It should be appreciated that the cathode port holes 226 provide inletand outlet passages in the form of tunnels for the fuel gases to flowthrough the bipolar plate assembly 200. A skilled artisan shouldunderstand that various configurations of the cathode channels 218, thefeed channels 222, and the cathode port holes 226 may be used within thescope of the present disclosure. It should also be recognized that thepresent disclosure is not limited to a particular flow field pattern,but has application to bipolar plate assemblies 200 independent of theflow field pattern.

With reference to FIGS. 3-4, the coolant side 208 of the formed cathodehalf plate 202 has a coolant active area 228. The coolant active area228 is disposed opposite the active area 216 of the same formed cathodehalf plate 202. The coolant side 208 further has support features 230,232. The support features 230, 232 are disposed opposite at least one ofthe feed region 210, 211 and the active area 216 of the same formedcathode half plate 202.

In should be understood that at least a portion of the coolant activearea 228 of the formed cathode half plate 202 is different from, and isnot constrained to correspond with, the cathode channels 218 of theactive area 216. This is facilitated by the formation of the formedcathode half plate 202 by molding or cutting manufacturing methods,which are different from stamping operations, and which stampingoperations are otherwise known to provide lands on one side of the platecorresponding with channels on the other side of the plate, andvice-versa.

Advantageously, the employment of different structure in the coolantactive area 228 relative to the active area 216 is believed to allow foran optimization or maximization of current density for the bipolar plateassembly 200 of the present disclosure. In particular, desirable currentdensity has been found where the cathode channels 218 are provided witha pitch (where the term “pitch” is defined as a sum of the channel widthand the land width) of about 1.5 mm or less. In a most particularembodiment, the cathode channels 218 may have a pitch of about 1 mm.

The very fine pitch for the cathode channels 218 of the presentdisclosure is believed to provide for superior current densitiescompared to conventional stamped metal bipolar plates. One of ordinaryskill in the art may also select other suitable relative pitches for thecathode channels 218 of the reactant side 206 and the coolant activearea 228 of the coolant side 208, as desired.

As nonlimiting examples, as shown in FIGS. 3-4, the support features 230in the coolant distribution area 210, 211 of the formed cathode halfplate 202 may include a plurality of pillars 230 or other supportstructures that permit the passage of coolant flow. The plurality ofpillars 230 may extend outwardly from the coolant side of the formedcathode half plate 202. As shown in FIGS. 3-4, the pillars 230 aredisposed opposite only the feed regions 210, 211 of the formed cathodehalf plate 202, and are not otherwise disposed opposite the active area216 of the formed cathode half plate 202. The pillars 230 may also bespaced apart from one another and arranged in an array or matrix orother patterns that permit the passage of coolant flow. For example, thepillars 230 may be disposed every 3 mm (3 mm×3 mm array with the pillars230 generally arranged in rows and columns). Similar arrays may beprovided with other distributions, for example 1 mm×1 mm arrays, 2 mm×2mm arrays, and 5 mm×5 mm arrays, for example. It should be understoodthat other arrangements and distributions of the pillars 230 may beemployed by a skilled artisan.

In illustrative embodiments of the present disclosure, each of theplurality of pillars 230 may have an average diameter of less than about0.2 mm. In further embodiments, the plurality of pillars 230 have anaverage diameter of less than about 1 mm. In particular embodiments,each of the pillars 230 may have an average diameter of less than about0.5 mm. Other dimensions for the pillars 230 may also be employed, asdesired.

Regardless of arrangement, configuration, or dimensions, it should beappreciated that the pillars 230 are adapted to abut and support theadjacent stamped metal anode half plate 204 that is nested with theformed cathode half plate 202, for example, as shown in FIGS. 6-11.Thus, a height, width, and general shape of each of the pillars 230 maybe selected by one skilled in the art depending on the desired nesteddimensions of the formed cathode half plate 202 with the stamped metalanode half plate 204. The pillars 230 thereby facilitate a distributionof coolant from an associated one of the header apertures 214 to thecoolant distribution area 228, even while the bipolar plate assembly 200is under compression typical with operation of the fuel cell stack 2.

With reference to FIG. 4, the support features 230, 232 on the coolantside 208 of the formed cathode half plate 202 may also include aplurality of support ribs 232. The support ribs 232 are disposed only inthe coolant distribution area 228 opposite the active area 216 of theformed cathode half plate 202. In particular, the support ribs 232 maybe spaced apart from, and oriented generally parallel with, one anotheron the coolant distribution area 228. The support ribs 232 are elongateand may be oriented along a length of the coolant distribution area 228between the headers 212, 214 of the formed cathode half plate 202. Thesupport ribs 232 may also be substantially linear in shape. However, askilled artisan may also select other suitable shapes and distributionsof the support ribs 232, as desired.

It should be understood that the support ribs 232 on the coolant side208 of the formed cathode half plate 202 may furthermore allow for theuse of thinner metal gauges, such as typical foil gauges, for thestamped metal anode half plate 204 of the present disclosure. Inparticular, the support ribs 232 may be configured to interact with andsupport an opposing surface of the stamped metal anode plate 204 asdescribed further herein.

As shown in FIG. 5, the stamped metal anode half plate 204 of thepresent disclosure is configured to be nested with and affixed to theformed cathode half plate 202. The stamped metal anode half plate 204has a fuel side 234 and a coolant side 236. The stamped metal anode halfplate 204 further has a pair of feed regions 238, 239 and a pair ofheaders 240, 241 with a plurality of header apertures 242, 243. Althoughdescribed primarily herewith with respect to a single one of the feedregions 238, a single one of headers 240, and a single set of headerapertures 242 on one side of the stamped metal anode half plate 204, itshould be appreciated that descriptions of features from the feed region238, the header 240, and the header apertures 242 likewise apply to theother feed region 239, the other header 241, and the other headerapertures 243.

Being formed by a stamping operation on a thin metal sheet or foil, itshould be understood that the stamped features (e.g., the channels andlands) on the fuel side 234 of the stamped metal anode half plate 204will have corresponding but opposite features (e.g., lands and channels,respectively) with otherwise the same or similar dimensions on thecoolant side 236 of the stamped metal anode half plate 204.

The fuel side 234 of the stamped metal anode half plate 204 has anactive area 244. The active area 244 has a plurality of anode channels246 formed therein. The anode channels 246 are adapted to distribute thefuel gases (e.g., hydrogen) across the active area 244. The anodechannels 246 also define a plurality of lands 248 disposed therebetween.

The feed region 238 of the stamped metal anode half plate 204 isdisposed between the active area 244 and the header 240. The feed region238 has a plurality of feed channels 250 formed therein. The feedchannels 250 also define a plurality of lands 252 disposed therebetween.

The feed region 238 further has anode port holes 254 formedtherethrough, which are in turn in communication with a one of theheader apertures 242 associated with the fuel gases. The feed channels250 are in communication with both the anode channels 246 and the anodeport holes 254. The feed channels 250 are adapted to transport the fuelgases between the active area 244 and the one of the header apertures242 associated with the fuel gases.

It should be appreciated that the anode port holes 254 provide inlet andoutlet passages in the form of tunnels for the fuel gases to flowthrough the bipolar plate assembly 200. A skilled artisan shouldunderstand that various configurations of the anode channels 246, thefeed channels 250, and the anode port holes 254 may be used within thescope of the present disclosure. It should also be recognized that thepresent disclosure is not limited to a particular flow field pattern,but has application to bipolar plate assemblies 200 independent of theflow field pattern.

As discussed hereinabove, the coolant side 236 of the stamped metalanode half plate 204 has a plurality of lands 258 corresponding with theanode channels 246. In turn, the lands 258 define a plurality of coolantchannels 260 on the coolant side 236 of the stamped metal anode halfplate 204. The plurality of lands 258 abut the coolant side 208 of theformed cathode half plate 202 upon assembly, for example, as shown inFIGS. 6-11.

With reference to FIG. 8, where the formed cathode half plate 202 hasthe support ribs 232 on the coolant side 208, the support ribs 232 maybe aligned with every other one of the coolant channels 260 on thecoolant side 236 of the stamped metal anode half plate 204. It should beappreciated that the support ribs 232 in such an arrangement provide forsufficient support of the stamped metal anode half plate 204 while alsopermitting for a sufficient amount of the coolant channels 260 to remainopen for transfer of the coolant therethrough. Other arrangements forthe support ribs 232, including embodiments without any support ribs 232and instead just an empty pocket, are also contemplated and consideredto be within the scope of the present disclosure.

With renewed reference to FIG. 5, the stamped metal anode half plate 204a flat or planar perimeter flange 262. The planar perimeter flange 262defines at least part of a sealing region of the stamped metal anodehalf plate 204 that is configured to abut and seal with a sealcombination 300 of the fuel cell stack 2 including a plate seal 302 anda membrane seal 304, for example, as shown in FIGS. 12-14.

It should further be understood that the plurality of anode channels 246formed in the stamped metal anode half plate 204 includes a plurality ofbranched feed channels 264 in the feed region 238 of the stamped metalanode half plate 204. The anode channels 246 may also include aplurality of linear anode channels 266 in the active area 244. Thelinear anode channels 266 may be oriented along the active area 244 ofthe stamped metal anode half plate 204. A skilled artisan willappreciate that the linear shape of the anode channels 266 mayadvantageously facilitate a cooperation of the opposing coolant channels260 with the support ribs 232 where also linear in shape, as describedhereinabove. However, although the anode channels 266 in the active area244 are shown in FIG. 5 as being linear between the feed regions 238,239, one of ordinary skill in the art may select other suitableconfigures for the anode channels 266 in the active area 244 of thestamped metal anode half plate 204, as desired.

With respect to the active areas 216, 244 of the bipolar plate assembly200, it should be appreciated that at least one of the active areas 216,244 may be have a coating (not shown). The coating may be adapted toprovide corrosion resistance, thermal conductivity, and optimizedelectrical conductivity and contact resistance, for example. Inembodiments where the active areas 216, 244 are coated, the coating mayfacilitate electrical conductivity.

As nonlimiting example, the coating may include noble metals, metaloxides, carbon and combinations thereof. Suitable noble metals forcoatings include gold (Au), silver (Ag), iridium (Ir), ruthenium (Ru),rhodium (Rh), osmium (Os), palladium (Pd) and platinum (Pt), forexample. In particular embodiments, the metal employed for the coatingof the active areas 216, 244 is gold (Au). Suitable metal oxides for thecoating, but are not limited to, hafnium dioxide (HfO₂), zirconiumdioxide (ZrO₂), aluminum oxide (Al₂O₃), tin oxide (SnO₂), tantalumpent-oxide (Ta₂O₅), niobium pent-oxide (Nb₂O₅), molybdenum dioxide(MoO₂), iridium dioxide (IrO₂), ruthenium dioxide (RuO₂) and mixturesthereof. The coatings are typically applied using any commerciallyavailable process. As nonlimiting examples, the coatings may be appliedby one of electroplating, electro-less plating, and physical vapordeposition. It should be understood that other suitable methods forapplying the coatings may be used as desired.

In particular embodiments, the coating may be hydrophilic and adapted tofacilitate a removal of liquid water from the active areas 216, 244during operation of the fuel cell stack 2. Suitable hydrophilic coatingsmay include the noble metal coatings as described herein and as known inthe art. As nonlimiting examples, the coating can include at least oneSi—O group, at least one polar group and at least one group including asaturated or unsaturated carbon chain. In further embodiments thecoating comprises at least one Si—O group and an Si—R group, wherein Rincludes a saturated or unsaturated carbon chain and the molar ratio ofSi—R groups to Si—O groups ranges from ⅛ to ½. The coating may also beapplied by any means sufficient for applying hydrophilic coatings.Suitable hydrophilic coatings can also include nanoparticles having asize ranging from 1 to 100 nanometers, wherein the nanoparticlescomprise a compound comprising a Si—O group, a saturated or unsaturatedcarbon chain and a polar group. It should be appreciated that otherhydrophilic coatings can also be used.

The hydrophilic coatings may be applied by any suitable methodincluding, but not limited to, laminating (such as by hot rolling),brushing, spraying, spreading, coil coating, silk screening, powdercoating, and screen printing. Multiple coats of the coating may also beapplied as desired.

In operation, and as described further hereinabove with respect to FIG.1, the hybrid bipolar plate assembly 200 of the present disclosure isemployed in the fuel cell stack 2. The fuel cell stack 2 may include aplurality of the MEAs 4, 6 arranged in a stacked configuration. Inaddition to a plurality of the bipolar plate assembly 200 and the MEAs4, 6 described hereinabove, the fuel cell stack 2 may further havenonconductive gaskets 28, 30 in the form of a membrane seal 304, forexample, as shown in FIGS. 13-14.

In a particular example, shown in FIGS. 12-14, a seal combination 300 ofthe fuel cell stack 2 may include a plate seal 302. The plate seal 302is adapted to hermetically seal or affix the formed cathode half plate202 with the stamped metal anode half plate 204, for example, as shownin FIGS. 6-10. The plate seal 302 may be formed from one of anelastomer, a compressible graphite, and an epoxy material, asnon-limiting examples, as also described hereinabove. Other suitablematerials and methods for forming the plate seal 302 may also beemployed within the scope of the disclosure.

In particular, the plate seal 302 is configured to be disposed aroundthe perimeter of the bipolar plate assembly 200, including bipolar plateheaders that are defined by the header apertures header apertures 214,215, 242, 243. However, as shown in FIG. 12, the plate seal 302 is notdisposed adjacent an inboard portion of the header apertures 214, 215,242, 243 associated with the coolant distribution. It should beappreciated that the absence of the plate seal 302 adjacent the inboardportion these header apertures 214, 215, 242, 243 permits for thedistribution of the coolant to the interior coolant distribution area ofthe bipolar plate assembly 200 in operation.

The seal combination 300 of the fuel cell stack 2 further includes amembrane seal 304, for example, as shown in FIG. 13. The membrane seal304 is disposed between the bipolar plate 200 and the MEA 4, 6. Inparticular, the membrane seal 304 is formed from an elastomer anddisposed around a perimeter of the bipolar plate assembly 200 and eachof the header apertures 214, 215, 242, 243. However, the membrane seal304 is also configured to be disposed around the header apertures 214,215, 242, 243 associated with the coolant distribution, as shown in FIG.13. The membrane seal 304 thereby militates against a leakage of coolantinto the active areas of the fuel cell stack 2.

As shown in FIG. 14, it should be appreciated that the membrane seal 304is generally overlaid with the plate seal 302 when each are present inthe fuel cell stack 2, and that the seals 302, 304 together circumscribeone of the diffusion medium layers 36, 38. In addition the diffusionmedium layers 36, 38 are of a predetermined size such that a perimeteredge of the one of the diffusion medium layers 36, 38 is laterallyspaced apart from each of the membrane seal 304 and the plate seal 302.This advantageously allows spaced for the stamped channels to un-nest inthat region between the perimeter edge of the diffusion medium layers36, 38 and the seal combination 300.

Advantageously, as shown in FIGS. 9-10 and 14, the plate seal 302 may beoffset from the membrane seal 304 in an inboard direction in front of atleast one of the anode and cathode header apertures 214, 215, 242, 243by a distance G. The width of the plate seal 302 at this location mayalso be narrower than the width of a corresponding portion of themembrane seal 304 at this location. For example, the width of the plateseal 302 may be about one-half (½) the width of the membrane seal. Thispermits for a smaller overall construction of the fuel cell stack 2,while also permitting tunnel flow to at least one of the cathode andanode port holes in operation. Likewise, a width of the plate seal 302may be narrower in front of the anode header to allow tunnel flow toaccess the anode ports.

The cooperation of the hybrid bipolar plate assembly 200 with one of theMEAs 4, 6 is further illustrated in FIGS. 6-11, which arecross-sectional views of an exemplary fuel cell stack 2 taken varioussection lines shown in FIG. 5.

In FIGS. 6-8, the stamped metal anode half plate 204 is illustratedhaving a flat perimeter in the sealing region. The stamped metal halfplate 204 also has the branched feed channels and the straight channelsthrough the active area with an elevation change from the feed region toactive area channels to nest into the back of the formed cathode halfplate 202. This in turn causes the lands on the coolant side of thestamped metal anode half plate 204 to abut and nest into the coolantside of the formed cathode half plate 202.

In particular, in FIG. 6, a long section view of a transition betweenthe feed region and the active area of the fuel cell stack 2 is shown.In FIG. 7, a cross section view of the fuel cell stack 2 in the activearea is shown, where the formed cathode half plate 202 is the embodimentshown in FIG. 3 without the support ribs 232. In FIG. 8, a cross sectionview of the fuel cell stack 2 in the active area is shown, where theformed cathode half plate 202 is the embodiment shown in FIG. 4 with thesupport ribs 232.

In FIGS. 9-11, section view of the cathode, anode, and coolant tunnelsand associated features for these regions are shown. The tunnels arebetween the cathode and anode half plates 202, 204 for all three fluids.The cathode has port holes in the formed cathode half plate 202 afterthe membrane seal into the start of the cathode feed channels. The anodehas port holes in the stamped anode half plate 204 after the membraneseal into the start of the anode feed channels. The coolant tunnelscontinue between the two half plates 202, 204 into the coolant feedregion. The bead feature (i.e., the rib on the coolant side 236 of anodehalf plate 204) along the plate seal 302 can be observed in the cathodeand anode tunnel sections shown in FIGS. 9 and 10. The coolant tunnelsections are shown in FIG. 11.

It should be appreciated that the bipolar plate assembly 200 of thepresent disclosure, having the stamped metal anode half plate 204 nestedinto the formed cathode half plate 202, advantageously provides tunnelfeatures in the formed cathode half plate 202. As disclosed hereinabove,sealing between the formed cathode half plate 202 and the stamped metalanode half plate 204 is provided by a) a compressed elastomeric plateseal 302, b) a compressed region of compliant graphite of the formedcathode half plate 202 itself, which forms the plate seal 302 and c)bonding of the metal of the stamped metal anode half plate 204 and theformed cathode half plate 202 with epoxy in the same region to form theplate seal 302.

Advantageously, the bipolar plate assembly 200 of the presentfacilitates a reduced fuel cell thickness compared to fuel cellsmanufactured with conventional formed bipolar plates. Improvedperformance with fine pitch cathode channels are obtained, however, withthe bipolar plate assembly 200 of the present disclosure. Minimizedthermal mass with reduced coolant volume is also obtainable compared toconventional fully stamped metal plates. This can be further reducedwith use of the coolant channel support ribs, particularly wherecompared to conventional nested metal half plates. The bipolar plateassembly 200 also may be manufactured at a reduced cost and mass withthinner metal for the stamped metal anode half plate being enabled bythe coolant channel support ribs from the coolant side of the formedcathode half plate.

While certain representative embodiments and details have been shown forpurposes of illustrating the invention, it will be apparent to thoseskilled in the art that various changes may be made without departingfrom the scope of the disclosure, which is further described in thefollowing appended claims.

1. A hybrid bipolar plate assembly for a fuel cell, comprising: a formedcathode half plate having a reactant side and a coolant side, a feedregion, and a header with a plurality of header apertures, the reactantside having an active area, the active area having a plurality ofcathode channels formed therein, the feed region disposed between theactive area and the header and having a plurality of feed channelsformed therein and cathode port holes formed therethrough, the feedchannels in communication with the cathode channels and the cathode portholes, the coolant side having a coolant distribution area disposedopposite the active area and support features disposed opposite at leastone of the feed region and the active area, and at least a portion ofthe coolant distribution area being different from and not correspondingwith the cathode flow channels of the active area; and a stamped metalanode half plate affixed to the formed cathode half plate, the stampedmetal anode half plate having a fuel side and a coolant side, a feedregion, and a header with a plurality of header apertures, the fuel sidehaving an active area, the active area having a plurality of anodechannels formed therein, the feed region disposed between the activearea and the header and having a plurality of feed channels formedtherein and anode port holes formed therethrough, the feed channels incommunication with the anode channels and the anode port holes, thecoolant side having a plurality of lands corresponding with the anodechannels, the lands defining a plurality of coolant channels on thecoolant side of the stamped metal anode half plate, the plurality oflands abutting the coolant side of the formed cathode half plate.
 2. Thehybrid bipolar plate assembly of claim 1, wherein the cathode channelshave a pitch of about 1.5 mm or less.
 3. The hybrid bipolar plateassembly of claim 2, wherein the cathode channels have a pitch of about1 mm.
 4. The hybrid bipolar plate assembly of claim 1, wherein thesupport features on the coolant side of the formed cathode half plateinclude a plurality of pillars extending outwardly from the coolant sideof the formed cathode half plate.
 5. The hybrid bipolar plate assemblyof claim 4, wherein the pillars are spaced apart from one another andarranged in an array.
 6. The hybrid bipolar plate assembly of claim 4,wherein the support features on the coolant side of the formed cathodehalf plate include a plurality of support ribs disposed in the coolantdistribution area.
 7. The hybrid bipolar plate assembly of claim 6,wherein the support ribs are spaced apart from and parallel with oneanother, and the support ribs are oriented along a length of the coolantdistribution area.
 8. The hybrid bipolar plate assembly of claim 7,wherein the support ribs are aligned with every other one of the coolantchannels on the coolant side of the stamped metal anode half plate. 9.The hybrid bipolar plate assembly of claim 1, wherein the stamped metalanode half plate has a sealing region with a planar perimeter flange.10. The hybrid bipolar plate assembly of claim 9, wherein the stampedmetal anode half plate has a bead feature disposed in the sealing regionadjacent to at least one of an anode header aperture and a cathodeheader aperture.
 11. The hybrid bipolar plate assembly of claim 1,wherein the plurality of anode channels formed in the stamped metalanode half plate includes a plurality of branched feed channels in thefeed region of the stamped metal anode half plate and a plurality oflinear flow channels oriented along the active area of the stamped metalanode half plate.
 12. The hybrid bipolar plate assembly of claim 11,wherein there is an elevation change from the branched feed channels inthe feed region to the linear flow channels in the active area to causethe lands on the coolant side of the stamped metal anode half plate toabut the coolant side of the formed cathode half plate.
 13. The hybridbipolar plate assembly of claim 1, wherein the formed cathode half plateis formed from graphite and the stamped metal anode half plate is formedfrom stainless steel.
 14. The hybrid bipolar plate assembly of claim 1,wherein the formed cathode half plate has a thickness of between about0.3 mm and about 1 mm.
 15. The hybrid bipolar plate assembly of claim14, wherein the stamped metal anode half plate has a thickness ofbetween about 0.25 mm and about 0.55 mm.
 16. A hybrid bipolar plateassembly for a fuel cell, comprising: a formed cathode half plate havinga reactant side and a coolant side, a feed region, and a header with aplurality of header apertures, the reactant side having an active area,the active area having a plurality of cathode channels formed therein,the feed region disposed between the active area and the header andhaving a plurality of feed channels formed therein and cathode portholes formed therethrough, the feed channels in communication with thecathode channels and the cathode port holes, the coolant side having acoolant distribution area disposed opposite the active area and supportfeatures disposed opposite at least one of the feed region and theactive area, and at least a portion of the coolant distribution areabeing different from and not corresponding with the cathode flowchannels of the active area, wherein the cathode channels have a pitchof about 1 mm or less, and wherein the support features on the coolantside of the formed cathode half plate include a plurality of pillarsextending outwardly from the coolant side of the formed cathode halfplate, wherein the formed cathode half plate has a thickness of betweenabout 0.3 mm and about 1 mm, and wherein the formed cathode half plateis formed from graphite; a stamped metal anode half plate affixed to theformed cathode half plate, the stamped metal anode half plate having afuel side and a coolant side, a feed region, and a header with aplurality of header apertures, the fuel side having an active area, theactive area having a plurality of anode channels formed therein, thefeed region disposed between the active area and the header and having aplurality of feed channels formed therein and anode port holes formedtherethrough, the feed channels in communication with the anode channelsand the anode port holes, the coolant side having a plurality of landscorresponding with the anode channels, the lands defining a plurality ofcoolant channels on the coolant side of the stamped metal anode halfplate, the plurality of lands abutting the coolant side of the formedcathode half plate, wherein the stamped metal anode half plate has asealing region with a planar perimeter flange, wherein the plurality ofanode channels formed in the stamped metal anode half plate includes aplurality of branched feed channels in the feed region of the stampedmetal anode half plate and a plurality of linear flow channels orientedalong the active area of the stamped metal anode half plate, wherein thestamped metal anode half plate has a thickness of between about 0.25 mmand about 0.55 mm, and wherein the stamped metal anode half plate isformed from stainless steel; and a plate seal disposed between andsealing the formed cathode half plate with the stamped metal anode halfplate, wherein the plate seal is formed from one of an elastomer, acompressible graphite, and an epoxy material, and is also disposedaround a perimeter of each of the formed cathode half plate and thestamped metal anode half plate.
 17. A fuel cell stack comprising: aplurality of membrane electrode assemblies arranged in a stackedconfiguration, each of the membrane electrode assemblies having apolymer electrolyte membrane with a cathode and an anode and associateddiffusion medium layers; and a hybrid bipolar plate assembly disposedbetween adjacent membrane electrode assemblies, the hybrid bipolar plateassembly including a formed cathode half plate and a stamped metal anodehalf plate, the stamped metal anode half plate affixed to the formedcathode half plate, the formed cathode half plate having a reactant sideand a coolant side, a feed region, and a header with a plurality ofheader apertures, the reactant side having an active area, the activearea having a plurality of cathode channels formed therein, the feedregion disposed between the active area and the header and having aplurality of feed channels formed therein and cathode port holes formedtherethrough, the feed channels in communication with the cathodechannels and the cathode port holes, the coolant side having a coolantdistribution area disposed opposite the active area and support featuresdisposed opposite at least one of the feed region and the active area,and at least a portion of the coolant distribution area being differentfrom and not corresponding with the cathode flow channels of the activearea, and the stamped metal anode half plate and affixed to the formedcathode half plate, the stamped metal anode half plate having a fuelside and a coolant side, a feed region, and a header with a plurality ofheader apertures, the fuel side having an active area, the active areahaving a plurality of anode channels formed therein, the feed regiondisposed between the active area and the header and having a pluralityof feed channels formed therein and anode port holes formedtherethrough, the feed channels in communication with the anode channelsand the anode port holes, the coolant side having a plurality of landscorresponding with the anode channels, the lands defining a plurality ofcoolant channels on the coolant side of the stamped metal anode halfplate, the plurality of lands abutting the coolant side of the formedcathode half plate.
 18. The fuel cell stack of claim 17, wherein each ofthe membrane electrode assemblies includes a membrane seal and thebipolar plate assembly includes a plate seal, the plate seal disposedbetween and sealing the formed cathode half plate with the stamped metalanode half plate, the membrane seal and the plate seal bothcircumscribing one of the diffusion medium layers, a perimeter edge ofthe one of the diffusion medium layers spaced apart from each of themembrane seal and the plate seal.
 19. The fuel cell stack of claim 18,wherein the membrane seal is formed from an elastomer and disposedaround a perimeter of the bipolar plate assembly and each of the headerapertures, the membrane seal abutting and sealing with one of thepolymer electrolyte membranes.
 20. The fuel cell stack of claim 19,wherein the plate seal is formed from one of an elastomer, acompressible graphite, and an epoxy material, and is also disposedaround the perimeter of the bipolar plate assembly, and a portion of theplate seal adjacent one of the header apertures for the anode isnarrower than a corresponding portion of the membrane seal adjacent theone of the header apertures for the anode, whereby tunnel flow to theanode port holes is permitted.